It is demanded to develop a method which can increase spectral sensitivity in the short wavelength region of green light and can improve the color reproducibility of photographic materials in the field of silver halide color photographic materials.
Conventional methods for increasing spectral sensitivity in the wavelength region of green light include the applications of photographic emulsions containing a combination of oxacarbocyanine and benzimidazolocarbocyanine (described in JP-A-59-116646 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), JP-A-59-116647, JP-A-59-140443 and JP-A-59-149346), a combination of oxacarbocyanine and oxathiacarbocyanine (described in JP-B-46-11627 (the term "JP-B" as used herein means an "examined Japanese patent publication") and JP-A-60-42750) and a combination of two or more oxacarbocyanines (described in JP-A-52-23931). However, spectral sensitivity in the short wavelength region of green light at 520 to 545 nm is low, and in any of these methods, it has been inconvenient to color reproducibility. Accordingly, it has been considered that sensitizing dyes having the maximum spectral sensitivity at 520 to 545 nm are further used in combination. Benzimidazolooxazolocarbocyanine (described in JP-B-44-14030) and dimethinemerocyanine (described in U.S. Pat. Nos. 2,493,743, 2,519,001 and 3,480,439) are conventionally known as sensitizing dyes having the maximum spectral sensitivity at 520 to 545 nm. However, emulsions containing benzimidazolooxazolocarbocyanine or dimethinemerocyanine have disadvantages in that fog is increased under high temperature conditions or under high temperature and humidity conditions after the coating of the emulsions, and sensitivity is lowered because of poor long-term stability after the coating of the emulsions.
There are known oxacarbocyanines, which have less inconvenience, having the maximum spectral sensitivity at 520 to 545 nm alone. Examples of the oxacarbocyanines are described in U.S. Pat. Nos. 2,521,705 and 2,521,959, 2,647,054 and JP-A-63-167348. However, the spectral sensitivity of these dyes has been still insufficient. Monomethinecyanines having 2-quinoline skeleton have the maximum spectral sensitivity at 520 to 545 nm. However, when they alone are used, sensitivity is low, and hence they are used in combination with benzimidazolocarbocyanine or oxacarbocyanine (described in JP-B-56-24939, JP-B-56-38936, JP-B-56-38940 and U.K. Patent 1,219,016). When these combinations are used, the region of-spectral sensitivity is shifted to a longer wavelength side, and hence good color reproducibility cannot be obtained. Accordingly, it has been demanded to develop a method which can increase spectral sensitivity in the short wavelength region of green light to obtain the true color reproducibility of color photographic materials.